The present invention relates to a battery.
A cylindrical lead acid battery is fabricated, for example, by spirally winding a strip-form positive electrode 21 and negative electrode 22 through a strip-form separator 23 to form a cylindrical electricity-generating element 24 as shown in FIG. 6, inserting this element 24 into a battery case (not shown), and sealing the case.
This electricity-generating element 24 formed by winding has current collecting lugs 21a and current collecting lugs 22a, which protrude on the upper side of the element 24 so as to be arranged on a straight line passing through the center of winding. The current collecting lugs 21a of the positive electrode 21 are arranged on one half of this straight line, i.e., on one side of the center of winding, while-the current collecting lugs 22a of the negative electrode 22 are arranged on the other half. Namely, the current collecting lugs 21a and 22a are arranged in such a manner that the current collecting lugs located on one side of the center of winding differ in polarity from those located on the other side. The current collecting lugs 21a of the positive electrode 21 are connected to a positive terminal through a positive-electrode strap (not shown) disposed to cover the current collecting lugs 21a. On the other hand, the current collecting lugs 22a of the negative electrode 22 are connected to a negative terminal through a negative-electrode strap (not shown).
The reasons why the current collecting lugs 21a and 22a are arranged on a straight line are explained below with respect to the current collecting lugs 21a of the positive electrode 21. With respect to the current collecting lugs 22a of the negative electrode 22, an explanation is omitted because the same explanation applies thereto.
In the case where the current collecting lugs 21a are arranged on a straight line as in FIG. 6, a linear strap can be used for connecting the current collecting lugs 21a thereto. However, if the current collecting lugs 21a are not arranged on a straight line, the strap should have a shape corresponding to the arrangement of the current collecting lugs and be larger than the linear one. Use of such a large positive-electrode strap is disadvantageous in that not only there is the possibility of contact with a negative-electrode strap but also the battery has an increased mass (weight) because the strap is made of, e.g., a lead alloy and is hence heavy. For these reasons, the current collecting lugs 21a are arranged on a straight line passing through the center of winding.
In order for the current collecting lugs 21a to be arranged on a straight line passing through the center of winding, the positive electrode 21 should have such a structure that the length over which the positive electrode 21 is spirally wound together with a separator 23 and a negative electrode 22 from one current collecting lug 21a to the next current collecting lug 21a to make one turn increases toward the outer side. This structure is further explained by reference to FIG. 7, which illustrates a grid 21b for the positive electrode 21 which has not been filled with an active material. This strip-form grid 21b, which has current collecting lugs 21a protruding on one of the longer sides, is located so that the distance D between two adjacent current collecting lugs 21a becomes longer toward the outer side. This distance D is determined, for example, in the following manner. The distance D between a current collecting lug 21a and the next current collecting lug 21a located on the outer side thereof is a value approximately satisfying the relationship
D=2xcfx80r 
wherein r is the distance between the former current collecting lug 21a and the center of winding. As a result, all the current collecting lugs 21a are arranged on a straight line passing through the center of winding.
In conventional positive electrodes 21, the current collecting lugs 21a have the same shape regardless of whether they are located in an inner region of the coil or in an outer region thereof. We found that the conventional positive electrodes have a problem that electricity-generating element 24 as a whole has an uneven distribution of the reaction of each active material. This problem is explained in more detail with respect to the case where charge/discharge current flows through a positive electrode 21 via current collecting lugs 21a. In an inner region of the coil, the area in which electricity should be collected by one current collecting lug 21a is smaller than in an outer region since the distance D between adjacent two of the current collecting lugs 21a in the inner region is small. Because of this, sufficient charge/discharge current can flow through the active material in the whole area via the current collecting lug 21a. 
In contrast, in an outer region of the coil, the area in which electricity should be collected by one current collecting lug 21a is large since the distance D between adjacent two of the current collecting lugs 21a in the outer region is large. Accordingly, sufficient charge/discharge current cannot flow through the active material in the whole area in this region via the current collecting lug 21a, which is the same shape as those in the inner region. In the outer region, the part of the active material which is located near the current collecting lugs 21a is preferentially used, and that part of the active material which is located apart from the current collecting lugs 21a remains unused. There is hence the possibility of a decrease in battery performance.
This problem applies not only to the positive electrode 21 but to the negative electrode 22 employing the grid 22b shown in FIG. 8, which has current collecting lugs 22a protruding therefrom.
Under the circumstances described above, an object of the invention is to provide a battery in which the electricity-generating element as a whole can have an even distribution of the reaction of each active material.
The invention provides a battery comprising an electricity-generating element comprising a strip-form positive electrode, a strip-form negative electrode, and a strip-form separator,
said positive electrode and said negative electrode being spirally wound through said separator and said positive electrode and said negative electrode respectively having current collecting lugs protruding from a side thereof,
wherein the pitches of the current collecting lugs become longer toward the outer periphery side, and the at least one current collecting lug that located on the outer side has a larger width than that located on the inner side.
In this battery, the electricity-generating element has a current collecting lug has a larger width than the adjacent current collecting lug located on the inner side thereof. Consequently, although the current collecting lugs in an outer region are located at a long pitch and the area to be covered by each current collecting lug in that region is wide, the charge/discharge current can sufficiently flow through the active material throughout the whole each area in that region. Therefore, the charge/discharge current can evenly flow through the electrode plates including their inner and outer parts, whereby the active materials can have an even reaction distribution.
The current collecting lugs of the positive electrode and those of the negative electrode are preferably arranged on the same line.
This linear arrangement is advantageous in that the strap to be connected to the current collecting lugs of the positive electrode or to the current collecting lugs of the negative electrode can have a linear shape and hence have a minimum size and mass (weight).
Furthermore, each current collecting lug preferably has a width L approximately satisfying the relationship L=rxc3x97xcex8, wherein r is the distance between the current collecting lug and the center of winding and xcex8 is a constant of central angle.
According to this constitution, although each of the current collecting lugs located in an outer region should cover a larger area, the width thereof L becomes larger without fail in proportion to the value of r, i.e., toward to the outer periphery side. Consequently, the charge/discharge current can be caused to flow evenly through the electrode plates including their inner and outer parts without fail, whereby the active materials can have an even reaction distribution.
The central angel xcex8 is desirably a xcfx80/6 radian or larger from the standpoint that even the innermost current collecting lug has a sufficient width, and is desirably a xcfx80/3 radian or smaller from the standpoint of preventing the straps from having a too large mass (weight) due to the too large widths of the current collecting lugs.